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I've come here looking for some help. I have a Kohler 23eoz marine generator that has suddenly started producing 400v instead of 230v. Most of the service facilities listed by Kohler marine are general purpose marine mechanics. They've tried thus far by just replacing parts not diagnosing the problem. I'm a little afraid of what that's going to cost me in parts, labor and time by the time they've fixed it.

Here's what I posted on one of the marine forums, just wondering if anyone here has any ideas.

Last sunday my 2003 Kohler 23eoz with about 1100 hours on it decided it was no longer a 240v generator and instead a 400v generator. It was putting out 199v per leg. This unfortunately resulted in frying two of my air conditioning units and two battery chargers.

I called the yard I use for service who dispatched a technician and in working with Kohler decided the generator needed a new rectifier. The board cost about $230 and my pessimism quickly kicked in. Rarely does a $230 part fix anything I break (or so I feel.) So today the part was replaced and low and behold the generator still produces a stead 400v. Now they are jumping to thinking the windings are the problem and it could need a new stator.

I´m wondering if others have come across this and might have any ideas about what would cause the generator to produce a seemingly stable 400v. I"m wondering if the governor could have failed. I wouldn´t think the voltage regulator would be in play because I wouldn´t expect a healthy generator to produce 400v at any time.

Thoughts? Ideas? Random tests I can try? Anyone know of a good stepdown transformer from 400v to 240? Kidding....

I´m a little punch drunk from a day of replacing the failed components in my AC system. That is now all back together but I´d like to get the generator straightened out before I fry another bunch of equipment.

Don't know kohler, but on Onans when the rotor or stator windings short gen usually makes less voltage output, not more. So I suspect it's not a winding short

My Guess is AC voltage reg (if it has one) has shorted and is applying full voltage to the feild. Or maybe reg sense leads to 120V have opened or are bad connection. Other posibility is gen gov is stuck and allowing engine to run at a much higher rpm than normal.

Gens without an inverter run at a constant rpm at all times to make a steady 60hz. If rpm is high then voltage will be too, unless it has a voltage reg to compensate for that. Might try measuring HZ , most people here use a $25 killawatt meter for that ( home depot).

Might need to use a step down transformer to run the killawatt meter at ~ 125 volt max. Or make a voltage divider from pair (or several) lightbulbs in series. My killawatt displays hz accurately down to ~ 70-80 VAC , below that display fades out to unreadable.

Thanks very much for the info. I've read the procedure for testing the voltage regulator unfortunately I don't have a variac with which to test. I'll start by testing the frequency of the power coming out of the generator. From there it sounds like I need a way to bench test the VRM. I'll figure that out.

I don't know how Kohler is wired , you have to look at the wiring , but If voltage reg has a voltage adjustment pot, you might try following: Instead of using a variac to vary sense input voltage to reg, feed sense leads 120V utility power and vary voltage adjust pot and see if voltage across the field leads responds **. Would expect for convenience you can do this with a substitute load for field on the reg instead of actual field winding .

It does indeed have a voltage pot. I'll try the test like you describe and see if I can get any variability out of it.

One thing I've been thinking about and not sure I know the answer but perhaps others do.... The generator appears to be producing 399v right now. Is it possible that the unregulated voltage would be this high? This seems like surprisingly high voltage for a generator designed to produce 230v.

No idea about a Kohler.
But on an Onan 6.5 kw NHE type rotor excitation voltage ( from reg) is ~ 18-60 VDC, while typical is 36. I think it only goes to 60 when it's fully loaded or a heavy full load is suddenly applied.

So seems there is some posibility of a very high voltage if reg fails at full output. Heard military gen regs are designed to fail at full output.

If rpm is also high that can contribute to higher voltage too.

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Just occurred to me, the pots may be dirty/bad. With reg installed in gen move the pot through its full range of adjustment several times. That sometimes gets onan regs working temporarily.

If you have a volt meter on gen output while you are adjusting the pots, if the voltage makes sudden jumps all over the place, then the pots are likely dirty. If you are handy with a soldering iron you can solder in some new pots.

From there you're going to want to check the sensing voltage to the regulator. This will be a direct connection from the output leads which are wires 3 & 4, which go to the terminals #2 & #3 on the regulator from the looks of the manual.

You should have whatever output voltage is on the sensing terminals. If output is 400 volts, you should see 400 volts. If it's 120 volts, you should see 120 volts. If you see nothing, that's why your generator is putting out 400+ volts. Here's why:

The regulator uses the sensing voltage to "see" what the output of the generator is. If sensing voltage is low, the regulator increases the output. This would be analogous to turning on an AC unit and having the voltage drop as a result. The regulator sees the voltage drop and sends more power to the generator via the exciter to produce more power to accept the AC load.

If the sensing leads are broken, disconnected, or there is an open circuit of some sort, the regulator sees 0 volts. Since it thinks the generator isn't producing any voltage, it goes full field, or, in a simpler sense, it "steps on the gas" to get the generator to produce more output. As a result of this condition the generator produces the maximum amount of power it can, which can be in excess of 400 volts.

If you start the unit up and see 400 volts on the sensing leads, the regulator is most likely at fault. It's going full field for no reason, in other words, it's stuck with it's foot on the gas.

To confirm this is the case, you could disconnect the exciter fields, which appear to be terminals #7 & #8 on the voltage regulator to remove all power from the generator. With the exciter disconnected, the generator should produce no power other than residual, which would be in the range of a few volts.